Joule Thief

[conradelektro]

I would like to "advertise" (again) a very good modification of the Joule Thief circuit which I copied from a person calling himself "groundloop" (see the attached drawing). For people who followed this thread a long time, this is no news. This post is intended for experimenters who joined more recently (like me).

This circuit (in comparison with the original Joule Thief circuit) runs with a reduced base current, which keeps the transistor cooler and also uses less power (because the rather high base current which just produces heat in the transistor is reduced to very little).

The power consumption is regulated by the capacitor (5 pF to 1000pF) rather than with a variable resistor. The resistor stays at 1 MOhm (or 100 KOhm for very low voltage and very low power applications).

Specially if one wants more power and a higher voltage power supply (e.g. 12 Volt), this circuit (with a low capacitance, e.g. C=20 pF) is very good.

But also on the "low end" (very little power and voltage, e.g. from an earth battery or other strange batteries) this circuit (with R=100K, C=1nF=1000pF, transistor=BC547N) works very well.

I want to convey, that many different cores can be used (with the original Joule Thief circuit and with the one proposed). Toroids are just one possibility. I personally like air cores because they are so simple and cheap, but I saw good videos on YouTube with Ferrite rods, ordinary transformer cores and fly back transformers. (They use the original Joule Thief circuit.)

The "problem" is the number of turns for L1, L2 (and L3, if any). This needs experimenting when using a certain core and certain lamps.

The choice of transistor depends primarily on the power one wants to get out of the Joule Thief. For high power (many LEDs, CFL, FL) one needs a power transistor so that it can take the load and does not overheat. For very low power applications (strange batteries) one wants a very sensitive transistor (which can not take a high load, only one LED). In both cases transistors with a high DC current gain are better (because the base current can be very low). Therefore I switched to Darlington Pairs when I want more power (TIP142 or BD681) and to the BC547N (not a Darlington, but high DC current gain, needs only 0.6 Volt) for very low power experiments with strange batteries. Many transistors are good. Some poeple have strong personal preferences, just ignore them. Power transistor or no power transistor, this is important for not overheating the transistor.

Greetings, Conrad

[Pirate88179]

a question if i can light a 3mm 5000mcd led to full brightness will that also light a 285.000mcd 10mm led the volage and current are about the same for each led

Nice job on the longevity testing.  This is a good question that you ask.  I did some experiments with my 265,000 mcd leds (10 mm) vs. 2,600 mcd leds and here is what I found.  The high rated leds were brighter BUT not 100 times by any means.  Maybe, at best, 1.5 times.  But, they pulled a lot more power.  So, I ended up being able to use about 10 of the lower rated leds and got a lot more light then one of the high rated ones and they lasted longer on a single AA.

But, as we always say here on this forum, try it and see what you get and then tell us.  Maybe you will see something different, maybe not.  But we will all learn something.

Bill

[dasimpson]

just had an idea for the ppl with mice problem well pirate has the answer
i just have the mod to matal plates side buy side the taser connects to them lets see the mice servive that

[dasimpson]

lol i have the exact same hellicopter they work like a peace of crap canerlised mine for batteyrs mag wire etc sorry the one i have is the 0807 one

@Altrez
Yep, ME TOOO, I wanna see a photo if this is possible, could you discribe the winding secondary please.

I have a small tiny inci wincy electric motor, smallest I have eva seen, its the tail rotor in a electric powered helicopter, I think I will raid it and connect it to my JT and see what happens, he he.

OK see if you can find it

jim

0808.jpg = tiny electric tail rotor motor close up
0806.jpg = small chopper, I hid it in plane sight
0807.jpg = Now where is the small chopper?

I been in the garden also today, I burried a chunk of aluminium, upon testing, it comes up with nothing, zero, zilch, hmmmmmmmmmmmm. This is where I have my earth battery, plates of iron, lead, copper and carbon, now 2 choppers are in the mix.

jim

[dasimpson]

i owe every one an apology you can charge batterys from a joule thief i was doing it wrong i did not relise after the bridge you had to have a cap and another diode to stop the battery dumping it's charge back into the cap

for this i am sorry think ill keep comments to mys self till i have read the hole thread uptodate